Let us learn about propagation on 80m band

Winter is approaching and we expect better contacts on lower bands like 80m and 160m. Only downside for propagation on lower bands now is the solar activity. With Solar Cycle 25 near its peak, or some say there will be two peaks, one now and another in 2026, we cannot expect that good propagation on lower bands. In general, higher bands are better during solar maxima. In winter months, atmospheric noise, mostly due to distant lightning is likely to be lesser than during summer storms. That is one reason why 80m band will be better during winter months. Atmospheric noise is more of a problem in lower bands than higher bands. Here we are considering the natural noise and not the urban noise due to ever so many devices pumping RF into the environment!

I still remember my early days in ham radio during 1986 or so, when I had to migrate to 80m from 40m due to low solar activity. That would have been the end of Solar Cycle 21 and beginning of Solar Cycle 22. I was having only a Philips Prestige vacuum tube radio as RX. So I was limited to 40 and 80m bands. The radio did not cover the higher amateur radio bands, though it was a four band radio in those days. When 40m propagation came down due to low solar activity, I started listening the EC net on 80m at 10 pm. Later I added an 80m coil to my VU2VWN QRP VFO and went on 80m, not as QRP, but as 120 W TX using my 3 x 807 homebrew setup. Antenna was on top of tall coconut trees and I could make contacts within my state and to the neighbouring state of Tamil Nadu in those days, on 80m CW/AM.

But now, I am not even able to hear the morning 80m net on 3600 kHz, though the net control station is just a few kilometers away. That is because the noise floor is quite high even with a much better commercial dedicated amateur radio FT-710. May be it will improve in the next two months as I could hear something in November 2024 as shown in the initial video clip. My 80m inverted V dipole has feedpoint at about 5.5 m and ends at 4m, because I am not at the same old location and there are no trees at all in the current compound. Recently I have elevated the middle of one limb of the 80m dipole up to 9m as that is the place where I have a fiber mast up on first floor terrace for other antennas. Still, I can hardly hear anything on 80m.

D-layer of the ionosphere can absorb 80m signals significantly during day time. As D-layer disappears at night, longer distance intercontinental contacts are feasible on 80m. During day time, 80m can achieve mainly local contacts in the range of a few hundred kilometers. At night the range may extend a few thousand kilometers. Coverage may be better at high latitudes, especially in winter, due to lower ionization by sun rays. As mentioned initially, during summer, distant lightning can contribute significantly to static noise and poor reception on 80m. Higher effective radiated power gives an advantage in overriding background noise. Very high antennas and and full legal limit power gives a definite advantage on 80m, both of which I do not have!

An important challenge in 80m operation is to have an antenna with low angle of radiation needed for long distance communication. Usual types of dipoles mounted lower than quarter wave length of 20m, will produce high angle of radiation, the so called ‘cloud-burners’. They will be useful only for short range communication by near vertical incidence skywave propagation. A vertical antenna for 80m needs to be 20m tall, which is difficult to construct. Dimensions can be reduced by adding a loading coil and electrically shortening the antenna. But that will lead to power losses through resistive heating of the coil wire.

As the maximum usable frequency (MUF) is seldom in the range of 3.5 MHz corresponding to the 80m band, sky wave propagation is not the problem. Rather, it is the high D-layer absorption during day time. So we have to ensure that the DX communication path is mostly through darkness, not involving the daytime part of the globe. There can also be good dark-side grey-line propagation along the twilight zone. Polar routes away from equatorial thunderstorms is a good option for 80m propagation. But these may need directional antennas or antenna arrays rather than simple dipoles. Grey line propagation on 80m is supposed to be most effective during the spring and autumn equinoxes.

During night, at higher latitudes, especially during winter, skip distance may be high, preventing shorter distance communication on 80m. Even though winter is better time for 80m, during peaks of solar cycle, auroral activity can make the band useless in high latitudes for hours together.